1. Field of the Invention
The present invention relates generally to an ophthalmic auxiliary instrument and, more particularly, to a fundus of eye observation auxiliary instrument for holding a non-contact type aspherical inverted image lens for observing a fundus of eye which instrument is used with a slit-lamp microscope. The present invention also relates to an ophthalmic system for observing a fundus of eye or a cornea by use of the same auxiliary instrument.
2. Related Background Art
A prior art will be explained with reference to FIGS. 7 to 10.
Referring to FIG. 7, the numeral 50 designates an examined eye (eyeball), 51 represents a fundus of eye, 70 denotes an aspherical inverted image lens for observing the fundus of eye, and 52 indicates the side of an objective lens of a slit-lamp microscope. FIG. 8 illustrates how the fundus of eye of the examined eye is observed through the aspherical inverted image lens 70 by using the slit-lamp microscope 52 in combination.
The slit-lamp microscope 52 is, as illustrated in FIG. 8, constructed of an illumination optical system 31 and an observation optical system 32. The illumination optical system 31 has a halogen lamp 21 and a slit stop 22 for forming a slit light beam from the light beams emitted by the halogen lamp 21.
Normally, the slit-lamp microscope 52 forms an image of the light beam emerging from the slit stop 22 on the cornea of an examined eye 50 or a crystal lens, and a lesion of a front eye part (ranging from the cornea to the crystal lens) is observed with the aid of the slit beam.
The slit beam exiting the slit stop 22 is, after passing through respective lenses, deflected in its optical path by the prism 23. The deflected slit beam is, after traveling through the aspherical inverted image lens 70, image-formed on the fundus 51 of the examined eye 50. The reflected beam from the fundus of eye 51, as illustrated in FIG. 7, again passes through the aspherical inverted image lens 70 and is then image-formed in a focal position L1. The image of the fundus of eye is observed in enlargement by an eyepiece element 26 as well as by an objective element 25 of the observation optical system 32 of the slit-lamp microscope 52. The slit beam from the slit-lamp microscope 52 is short of a quantity of illumination light as an illumination light beam with which the fundus of eye is illuminated. For this reason, the slit beam from the slit-lamp microscope 52 is temporarily is image-formed in the focal position L1, and the slit beam image-formed in the focal position L1 is then image-formed by the aspherical inverted image lens 50, thereby obtaining a light quantity enough for observing the fundus of eye.
As a matter of fact, when observing the image of the fundus of eye, the aspherical inverted image lens 70 is held with a hand and moved to a position in front of the examined eye but spaced away a predetermined distance, i.e., a so-called W.D (Working Distance) therefrom, and, further, an optical axis of the examined eye 50 is made coincident with an optical axis of the aspherical inverted image lens 70. At this time, the examiner manipulates the slit-lamp microscope 52 with the other hand to make the optical axis of the slit-lamp microscope 52 coincident with the optical axis of the aspherical inverted image lens. Then, the eyepiece element 26 and the objective element 25 including the observation optical system 32 of the slit-lamp microscope 52 are moved in the optical-axis directions to adjust the focal point, and the image of the fundus of eye is observed. Thus, considerably laborious operations must be performed.
Then, facilitating such laborious operations as much as possible may involve the use of a variety of holders for holding the aspherical inverted image lens 70. FIG. 9 is a view illustrating one example of an external configuration of the slit-lamp microscope 52 equipped with the holder for the aspherical inverted image lens 70. A holder 61 is attached to the slit-lamp microscope 52 in this example. This holder 61 is so structured as to be movable in only a given range in the arrowed directions in FIG. 9 with respect to a mounting member 60 mounted to an upper portion of the slit-lamp microscope 52. Further, the holder 61 is always biased by spring action in the direction of the examined eye 50 and pushed against a W.D setting member 62 fitted to a forehead contact member 63.
The W.D setting member 62 is supported with respect to the forehead contact member 63 so that a pull-out quantity is adjustable on the side of the microscope 52. Accordingly, it is possible to adjust a distance between the aspherical inverted image lens 70 and the examined eye 50.
In this case, the optical axes of the slit-lamp microscope 52 and the aspherical inverted image lens 70 are made coincident beforehand by use of the holder 61, and hence the examiner makes it coincident with an optical axis of the examined eye 50 by use of a joy stick 64. Further, the slit-lamp microscope 52 is moved in the optical-axis directions (in the arrowed directions in FIG. 9), thus adjusting the focal point.
FIG. 10 shows a construction of the slit-lamp microscope 52 equipped with another type of holder. In the slit-lamp microscope 52 in this example, a holder 64 is attached to a chin sustainer rod 53. With the thus constructed holder 64, it is feasible to previously make the optical axis of the examined eye 50 coincident with the optical axis of the aspherical inverted image lens 70 and the optical axis of the slit-lamp microscope 52 unless the examinee moves the face from a chin sustainer 54 of the chin sustainer rod 53.
According to the construction of the slit-lamp microscope 52 including the above holder, the examiner has no necessity for holding the aspherical inverted image lens 70, and the operations are facilitated to some extent.
In the case of having the holders as shown in FIGS. 9 and 10, however, the optical axis of the aspherical inverted image lens 70 can be made easily coincident with the optical axis of the slit-lamp microscope 52. But, if the examinee moves the face even slightly, the optical axis of the slit-lamp microscope 52 deviates from the optical axis of the examined eye 50 (pupil), and besides W.D also changes. Hence, there arises a problem in which when observing the image of the fundus of eye, W.D has to be reset as well as readjusting the coincidence of the optical axes, and the laborious operations are required.